The market for returnable and refillable PET carbonated soft drink (CSD) bottles has enjoyed significant growth worldwide since its introduction by Continental PET Technologies in 1987. These returnable/ refillable bottles have been commercialized throughout much of Europe, Central and South America, and are now moving into the Far East market.
Returnable and refillable bottles reduce the existing landfill and recycle problems associated with disposable plastic beverage bottles. In addition, a refillable bottle permits the entry of a safer, lighter-weight plastic container into those markets, currently dominated by glass, where legislation prohibits use of non returnable packages. The goal is to produce a refillable bottle having the necessary physical characteristics to withstand numerous refill cycles, and which is still economical to produce.
Generally, a refillable plastic bottle must maintain its functional and aesthetic features over a minimum of 10 and preferably over 20 cycles or loops to be considered economically feasible. A loop is comprised of (1) an empty hot caustic wash followed by (2) contaminant inspection and product filling/capping, (3) warehouse storage, (4) distribution to wholesale and retail locations and (5) purchase, use and empty storage by the consumer followed by eventual return to the bottler. This cycle is illustrated in FIG. 1.
Returnable/refillable containers must exhibit several key criteria in order to achieve commercial viability. These include:
1. high clarity (transparency) to permit on line visual inspection; PA1 2. dimensional stability over the life of the container; and PA1 3. resistance to caustic wash induced stress cracking and leakage.
A known commercial returnable/refillable CSD container is formed of a single layer of polyethylene terephthalate (PET) containing 3-5% comonomer, such as 1,4-cyclohexanedimethanol (CHDM) or isophthalic acid (IPA). The preform, from which this bottle is blown, has a wall thickness on the order of 5-7 mm, or about 2-2.5 times that of a preform for a disposable 1-way bottle. This greater preform thickness provides the greater average bottle wall thickness (i.e., 0.5-0.7 mm) required for abuse resistance, based on the desired PET planar stretch ratio of 6-10:1, for bottle dimensional stability over time. The high copolymer content prevents visual crystallization, i.e., haze, from forming in the preform during the injection molding process. Excessive preform haze is undesirable because it hampers the commercial on line visual inspection process required for returnable/refillable beverage containers.
The known commercial CSD container has a demonstrated field viability in excess of 20 refill trips at caustic wash temperatures of 60.degree. C. Although successful, there exists a commercial need for an improved container that permits an increase in wash temperature capability to 65.degree. C. and preferably to 70.degree. C. or greater, along with a reduction in product flavor carryover. The latter occurs when flavor ingredients from a first product (e.g., root beer) migrate into the bottle sidewall and subsequently permeate into a second product (e.g., club soda) on a later fill cycle, thus influencing the taste of the second product. An increase in wash temperature is desirable to increase the effectiveness and/or reduce the time of the caustic wash and may be required with certain food products such as juice and milk.
Thus, it would be desirable to increase the allowable caustic wash temperature above 60.degree. C. for a returnable bottle having a lifetime of at least 5 refill trips and preferably in excess of 10 or 20 refill trips, and to reduce the product flavor carryover between refill trips. These and other objects are achieved by the present invention as set forth below.